Could also be a delayed carb flu. From what I've read here, sometimes carb flu kicks in right about three weeks.
If it IS carb flu, don't worry, it will be gone in two weeks and you'll have a LOT of energy for P90x2. Hang in there and DON'T increase the carbs yet. If you don't feel more energy in 10 days or so, then yes you probably need a few more carbs.
5'0" female, 44 years old. Started Primal October 31, 2011, at a skinny fat 111.5 lbs. Low weight: 99.5 lb on a fast. Gained back to 115(!) on SAD chocolate, potato chips, and stress. Currently keeping food tracker.
I (try to) follow by-the-book primal as advocated by Mark Sisson, except for whey powder and a bit of cream. I advocate a two-month strict adjustment for newbies. But everybody is different and should tweak Primal to their own needs.